Decreased levels of cell cycle inhibitor p27Kip1 due to excessive degradation occur in a variety of aggressive human tumors. Since reduced p27 expression has been associated with a poor prognosis in many human cancers and resistance to certain anti-tumor therapies, it has been postulated that elevation of p27 expression could improve prognosis and perhaps even provide a cure for malignant cancers. However, this concept has not been proven or rigorously tested largely due to the absence of specific small molecule inhibitors that perturb abnormal reduction in p27 levels. The abundance of p27 is primarily controlled by the ATP-dependent ubiquitin-proteasome pathway. SCFSkp2 is the major ubiquitin E3 ligase responsible for degradation of p27. Therefore inhibition of SCFSkp2 E3 ligase activity is expected to enhance p27 accumulation. The overall goals of this application are to investigate unique enzymatic mechanisms of SCFSkp2 E3 ligase that are amenable to chemical perturbation and develop specific reagents for chemical genetic dissection of the function of SCFSkp2 in cancer biology. Understanding the detailed and unique mechanism by which SCFSkp2 promotes ubiquitination of p27 is essential for developing highly selective therapeutic strategies to increase p27 levels with minimal side effects. Identifying specific small molecule inhibitors of p27 degradation is a first step towards evaluating whether inhibition of p27 degradation would be an effective anti-cancer therapy approach and translating what we have learned about the basic mechanisms of p27 degradation into potential new drug leads in cancer biology. PUBLIC HEALTH RELEVANCE: Excessive degradation tumor suppressing protein p27 in primary cancer tissue correlates with poor survival as well as poor response to chemotherapies. The goal of this proposal is to understand the molecular processes associated with abnormal degradation and search for drug-like molecules to prevent this degradation. Our studies could lead to novel therapy for malignant cancers and improve prognosis of patient with aggressive tumors.